In the field of magnetic disk media, it was a standard that 2 MB of MF-2HD using Co-modified iron oxide is mounted in a personal computer. Nowadays, however, the 2-Mbyte capacity of such a hard disk is said to be no longer sufficient because recent years have seen a sharp increase in volume of data to be addressed, and it is desired to enlarge the capacities of flexible disks. On the other hand, a magnetic disk medium made up of a thin magnetic layer and a functional non-magnetic layer has been developed, and 100 MB-class flexible disks are coming along. For instance, the magnetic disk medium disclosed in JP-A-10-21530 contains such features.
In the document cited above, it is defined that the magnetic disk medium, wherein a non-magnetic support, a substantially non-magnetic grounding layer and a magnetic layer containing a ferromagnetic metal or hexagonal ferrite powder dispersed in a binder are arranged in order of mention, has a specific relation between the thickness of the non-magnetic support and the outermost diameter of the recording area; as a result, the medium is successful in achieving high output and stable head penetration characteristic even in high-density recording. While the penetration evaluation in the document is made at a line recording density of 90 kfci, the disk medium cannot ensure satisfactory penetration characteristic when the evaluation is made at line recording densities higher than 90 kfci. Further, in the case of a magnetic disk medium not greater than 50 mm in diameter, or the so-called small-diameter disk, the attainment of sufficient recording capacity necessitates extending the recording area farthest toward the internal diameter side; as a result, head penetration on the internal diameter side becomes unstable.
When reproduction is performed using a highly sensitive magnetic reluctance head (an MR head) in particular for the purpose of heightening a recording density and not a traditional magnetic induction head, hitherto known magnetic disk media make high level of noises, so it is difficult for them to offer satisfactory performances.
Under recent circumstances where portable computer equipment, such as notebook PCs, and hand-held video recorders have rapidly come on strong, it has been desired to miniaturize magnetic recording media also. For instance, reduction in disk diameter to 50 mm or below makes it possible to apply the disks to PCMCIA card slots of personal computers. Although it is required for the disks to have recording capacities of at least several hundred megabytes equivalent to those of CD-ROM and CD-R, the reduction in disk diameter result in reduction of recording area, so it is difficult for the disks to meet two contrary requirements, attainment of high capacity and miniaturization.